Changes in nestedness in experimental communities of soil fauna undergoing extinction

Nestedness is the degree to which a set of communities represent different-sized subsets from the same ordered composition of species. Strong nestedness has been associated with communities presumably ordered by extinction – landbridge islands, habitat fragments – but development of nestedness in such systems due to extinction over time has rarely been followed. We examined the effects of local extinction on the nested structure of experimentally isolated nematode and microarthropod communities. Experiments were conducted in Georgia, USA, intact soil and litter microcosms, and Derbyshire, UK, in situ moss microecosystems. Nestedness increased initially, as predicted, but there was evidence of a decline in nestedness later in both experiments. Increasing nestedness was consistent with predictable losses of species, such as loss of less common species, predators, or species of large body size. We hypothesize that the later phase of declining nestedness was due to increasing disorder in species’ chance of extinction as the experiments progressed, with the resulting stochastic differentiation of communities reducing nestedness.